a) Field of the Invention
This invention relates to a triple-probe plasma measuring apparatus for industrial application of various plasma-application devices for accurately measuring or monitoring electron temperature and electron density of plasma.
b) Description of Related Art
In case of the application of plasma technique, it is necessary to instantaneously diagnose various quantities in plasma, particularly electron temperature and electron density. The so-called "triple-probe method" as a method for plasma diagnosis and a plasma measuring apparatus using this method is considered to be the most effective one, because it is capable of indicating at once these variables on indicating instruments.
This diagnostic method is effected by placing three probes, all having an equal area, in a juxtaposed relationship, at a location which is considered to be at an equi-potential level within the plasma, and by applying different voltages to these probes.
The triple-probe method has a ground of its establishment on the assumption that plasma is uniformly distributed in space, and that space potentials are respectively equal at positions where these three probes are present. In reality, however, it is almost rare that the space potentials are equal at those positions where the three probes are located. Rather, due to a slight potential difference existing between the adjacent probes, an error in the measured values was inevitable.